Currently, in an automatic blistering machine, a continuous band of heat-weldable material, or of aluminium, is driven to move forward through different working stations in the following order: a forming station, where receptacles, or blisters, are made in the band, a station, where the products are fed and the blisters are filled with the products, a station, where the upper surface of the band is sealed, and a station, where the pieces of the band containing a predetermined number or blisters, and consequently of products, are cut, each of these pieces forming a blister pack.
A unit is situated at the above feeding and filling station for feeding products and introducing them into the blisters. The above unit assures a correct filling of all the blisters, as well as the integrity of the products, so as to reduce jams and wastes of products, all this while maintaining the required high production speed.
Among different proposed solutions, one particularly advantageous is described in the International Patent Application PCT Num. WO 01/42088 of the same Applicant.
According to this solution, a unit for feeding products to a blister band situated below includes basically selection means which form a plurality of longitudinal channels, arranged in such a way as to define an oscillating grid and aimed at receiving products coming from the hopper situated above.
The selecting means are connected to suitable oscillating means, which generate a relative oscillating movement, crosswise and/or longitudinally, between the selecting means and the blister band opposite thereto, so as to facilitate stable introduction of the products present in the longitudinal channels, falling down into the corresponding blisters formed in the band.
A system of this kind requires overfeeding of products; therefore, in a fixed interval of time, the hopper must feed the selecting means with a number of products exceeding the number of blisters facing the grid in this interval of time.
Then, downstream of the selecting means, the exceeding products, which are not yet introduced into the blisters, are usually conveyed, by suitable collecting means, to the feeding hopper and then re-cycled.
The above described unit is functionally efficient, in particular as regards filling of blisters, which are usually sized as the products they must contain, i.e. the dimensions of the blister are slightly bigger than the dimensions of the product; the difference between the dimensions of the blister and the product facilitates the product introduction, but prevents more products from being introduced into the same blister.
In some cases, an product must be introduced in a blister much bigger than it is necessary in normal situation, i.e. in order not to modify the dies in the blister forming station: in this situation, known devices of the above described type do not manage to prevent two or more products, instead of only one, from entering each blister.
In other cases, blisters filling operation must be performed with bigger care with respect to the unit described in the above mentioned International Patent Application PCT Num. WO 01/42088, or other known devices, in order to protect the products integrity.
This necessity is more frequent with products like tablets, which are rougher and more friable than sugarcoated pills and less sliding with respect thereto, or in situations in which aluminium band is used, less resistant to denting than the band of plastic material.